1. Field of the Invention
This invention relates to endoscopic surgical instruments. More particularly, this invention relates to super-elastic jaw assemblies for multiple sample endoscopic instruments.
2. State of the Art
Endoscopic biopsy procedures are typically performed with an endoscope and an endoscopic biopsy forceps device (bioptome). The endoscope is a long flexible tube carrying fiber optics and having a narrow lumen through which the bioptome is inserted. The bioptome typically includes a long flexible coil having a pair of opposed jaws at the distal end and manual actuation means at the proximal end. Manipulation of the actuation means opens and closes the jaws. During a biopsy tissue sampling operation, the surgeon guides the endoscope to the biopsy site while viewing the biopsy site through the fiber optics of the endoscope. The bioptome is inserted through the narrow lumen of the endoscope until the opposed jaws arrive at the biopsy site. While viewing the biopsy site through the fiber optics of the endoscope, the surgeon positions the jaws around a tissue to be sampled and manipulates the actuation means so that the jaws close around the tissue. A sample of the tissue is then cut and/or torn away from the biopsy site while it is trapped between the jaws of the bioptome. Keeping the jaws closed, the surgeon withdraws the bioptome from the endoscope and then opens the jaws to collect the biopsy tissue sample.
A biopsy tissue sapling procedure often requires the taking of several tissue samples either from the same or from different biopsy sites. Unfortunately, most bioptomes are limited to taking a single tissue sample, after which the device must be withdrawn from the endoscope and the tissue collected before the device can be used again to take a second tissue sample. The single-sample limitation of most bioptomes is due to the limited space between the biopsy forceps jaws. Several attempts have been made to provide an instrument which will allow the taking of several tissue samples before the instrument must be withdrawn and the samples collected. Problems in providing such an instrument include the extremely small size required by the narrow lumen of the endoscope and the fact that the instrument must be flexible in order to be inserted through the lumen of the endoscope. Thus, several known multiple sample biopsy instruments are precluded from use with an endoscope because of their size and rigidity. These include the "punch and suction type" instruments disclosed in U.S. Pat. No. 3,989,033 to Halpern et al. and U.S. Pat. No. 4,522,206 to Whipple et al. Both of these devices have a hollow tube with a punch at the distal end and a vacuum source coupled to the proximal end. A tissue sample is cut with the punch and suctioned away from the biopsy site through the hollow tube. It is generally recognized, however, that suctioning tissue samples through a long narrow flexible bioptome is virtually impossible.
Copending application U.S. Ser. No. 08/189,937 discloses an endoscopic multiple sample bioptome which allows for the taking of multiple samples before removal of the bioptome from the endoscope. The multiple sample bioptome includes a hollow outer member and an axially displaceable inner member extending therethrough. The proximal ends of the outer and inner members are coupled to an actuator for axially displacing one relative to the other. The distal end of the outer member is coupled to one of a cylinder having a sharp distal edge and a jaw assembly, while the distal end of the inner member is coupled to the other. The jaw assembly includes a pair of opposed, preferably toothed jaw cups each of which is coupled by a resilient arm to a base member. The arms are bent to urge the jaws away from each other. The base member is mounted inside the cylinder and axial movement of the jaw assembly and cylinder relative to each other draws the arms into the cylinder (or extends the cylinder over the arms) and brings the jaw cups together in a biting action. In this manner, multiple samples from a patient can be taken and stored within the jaw assembly before needing to retrieve the bioptome from the patient.
A family of alloys known to exhibit unusual elasticity and flexibility properties has recently been identified as having useful practical applications. These alloys specifically exhibit what is called the shape memory effect. This effect provides that if such an alloy is plastically deformed from its original shape at one temperature, it will completely recover its original shape on being raised to a higher temperature. In recovering their shapes these alloys can produce a displacement or a force, or a combination, as a function of the temperature. Due to the unique atomic structure necessary for the memory shape effect to take place, these alloys exhibit other properties as well, such as super-elasticity or pseudo-elasticity.
The type of transformation which occurs in the shape memory alloys is known as a martensitic transformation and changes the material from a high temperature form, called austenite, to a low temperature form called martensite. For a given shape memory alloy, the transformation between martensite form and austenite form occurs at a predictable temperature, known as the transformation temperature.
In order for an alloy to exhibit the shape-memory effect, it must first be bent into the shape to be "memorized" at room temperature. The alloy is then heated until it assumes a high-temperature configuration called the beta or parent phase, where the crystal structure of the metal assumes its austenite form which it will "remember". Next, the alloy is rapidly cooled so that the atoms in the alloy rearrange themselves into the crystal form of martensite. The alloy may then be bent into a new shape which it will maintain as long as the temperature remains below the transformation temperature. If the alloy is subsequently reheated above its transformation temperature so that the alloy molecular structure reverts to an austenite form, it will recover its previously memorized shape. Shape memory alloys exhibit significantly increased resiliency relative to their non-superelastic counterparts, because the atoms of the memory metal shift back and forth between martensite and austenite forms, and do not slip into new dislocated configurations as is the case with normal metals.
Useful temperature independent properties are also exhibited by memory-shape alloys. In an alloy that has a beta phase capable of producing martensite under stress, one can observe an unusual elastic property called super-elasticity or pseudo-elasticity. In a typical alloy with this property, the metal exhibits normal elastic behavior under stress (that is, it gets longer in some dimensions) until the critical stress is reached at which point martensite molecular structures begin to form. With further stress, the specimen continues to elongate, as if it were being plastically deformed. When the stress is removed, the martensite structure reverts to the parent phase, or austenite structure, and the metal contracts to its original dimensions, showing no permanent deformation.
Presently, the applications of shape memory materials in medical apparatuses are very limited. U.S. Pat. No. 4,925,445 to Sakamoto et al. discloses a guide wire for a catheter, where the guide wire has a rigid body and a flexible distal end made of a memory-shape metal alloy with the super-elastic properties described above. The distal end of the wire is curved back such that a blunt forward tip is formed. With a super-elastic distal end, the guide wire can be guided through the blood vessel of a patient without the risk of permanently deforming the tip of the wire, which could result in the tearing of the blood vessel walls or in the misguiding of the wire. U.S. Pat. No. 5,254,130 to Poncet et al., similarly uses a memory-shaped alloy as a push rod and steering means for steering a distal clevis and attached end effectors. As the push rod is extended outside of the housing where it is held prior to deployment, the push rod assumes a remembered configuration relative to the straight housing, and hence steers the end effectors to a desired position. Other than the steering functions disclosed in the Sakamoto et al. and Poncet et al. patents, however, the super-elasticity of shape memory alloys has not been used in medical apparatus of the art.